The ANSS event ID is aka2026mnmqfw and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026mnmqfw/executive.
2026/06/26 05:23:10 64.830 -147.411 16.7 3.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/06/26 05:23:10.0 64.83 -147.41 16.7 3.1 Alaska
Stations used:
AK.H24K AK.HDA AK.NEA2 AK.POKR AK.PPD IM.IL31 IU.COLA
Filtering commands used:
cut o DIST/3.3 -20 o DIST/3.3 +20
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.25 n 3
Best Fitting Double Couple
Mo = 4.90e+20 dyne-cm
Mw = 3.06
Z = 21 km
Plane Strike Dip Rake
NP1 240 75 -35
NP2 340 56 -162
Principal Axes:
Axis Value Plunge Azimuth
T 4.90e+20 12 294
N 0.00e+00 52 40
P -4.90e+20 35 195
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.30e+20
Mxy -2.55e+20
Mxz 2.63e+20
Myy 3.71e+20
Myz -3.17e+19
Mzz -1.40e+20
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########--------------
##############--------------
################--------------
####################--------------
###################------------##
# T #####################---##########
## ###################--##############
####################-------#############
##################-----------#############
###############---------------############
#############-----------------############
##########---------------------###########
#######-----------------------##########
#####-------------------------##########
##---------------------------#########
----------------------------########
------------ ------------#######
---------- P -----------######
--------- -----------#####
-------------------###
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Global CMT Convention Moment Tensor:
R T P
-1.40e+20 2.63e+20 3.17e+19
2.63e+20 -2.30e+20 2.55e+20
3.17e+19 2.55e+20 3.71e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260626052310/index.html
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STK = 240
DIP = 75
RAKE = -35
MW = 3.06
HS = 21.0
The NDK file is 20260626052310.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Map showing station locations used for computing the ML's. No distinction is made whether the vertical (Z) or horizontal (H) components were used.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) the waveform inversion are shown in the next figure.
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The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green's functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.
The observed and predicted traces are filtered using the following gsac commands:
cut o DIST/3.3 -20 o DIST/3.3 +20 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.25 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 55 75 -25 2.20 0.2208
WVFGRD96 2.0 230 50 -40 2.42 0.2651
WVFGRD96 3.0 265 40 35 2.49 0.2728
WVFGRD96 4.0 265 45 40 2.55 0.2938
WVFGRD96 5.0 330 70 -60 2.60 0.2847
WVFGRD96 6.0 75 25 20 2.67 0.2963
WVFGRD96 7.0 85 45 30 2.71 0.3085
WVFGRD96 8.0 85 40 30 2.82 0.3241
WVFGRD96 9.0 85 40 30 2.85 0.3279
WVFGRD96 10.0 90 45 45 2.90 0.3207
WVFGRD96 11.0 75 65 35 2.92 0.3289
WVFGRD96 12.0 75 70 35 2.95 0.3518
WVFGRD96 13.0 70 80 35 2.98 0.3761
WVFGRD96 14.0 70 85 40 3.00 0.4074
WVFGRD96 15.0 240 80 -45 3.01 0.4309
WVFGRD96 16.0 240 80 -45 3.03 0.4635
WVFGRD96 17.0 240 75 -45 3.03 0.4763
WVFGRD96 18.0 240 75 -40 3.05 0.4908
WVFGRD96 19.0 240 75 -40 3.05 0.5007
WVFGRD96 20.0 240 75 -35 3.05 0.4887
WVFGRD96 21.0 240 75 -35 3.06 0.5007
WVFGRD96 22.0 240 75 -35 3.06 0.4935
WVFGRD96 23.0 240 75 -35 3.06 0.4846
WVFGRD96 24.0 240 75 -35 3.06 0.4844
WVFGRD96 25.0 240 75 -30 3.06 0.4706
WVFGRD96 26.0 240 75 -35 3.06 0.4662
WVFGRD96 27.0 245 80 -30 3.08 0.4688
WVFGRD96 28.0 245 80 -25 3.08 0.4675
WVFGRD96 29.0 245 80 -25 3.08 0.4701
WVFGRD96 30.0 245 80 -30 3.07 0.4593
WVFGRD96 31.0 245 80 -30 3.07 0.4549
WVFGRD96 32.0 245 75 -25 3.05 0.4517
WVFGRD96 33.0 245 75 -25 3.05 0.4560
WVFGRD96 34.0 245 70 -30 3.05 0.4621
WVFGRD96 35.0 245 70 -30 3.06 0.4718
WVFGRD96 36.0 240 65 -35 3.05 0.4754
WVFGRD96 37.0 240 65 -35 3.06 0.4683
WVFGRD96 38.0 245 70 -30 3.07 0.4568
WVFGRD96 39.0 245 75 -15 3.09 0.4561
WVFGRD96 40.0 245 65 -30 3.13 0.4510
WVFGRD96 41.0 245 65 -35 3.15 0.4451
WVFGRD96 42.0 245 65 -30 3.16 0.4377
WVFGRD96 43.0 245 70 -20 3.18 0.4355
WVFGRD96 44.0 245 70 -20 3.19 0.4361
WVFGRD96 45.0 245 70 -25 3.21 0.4332
WVFGRD96 46.0 245 70 -20 3.21 0.4271
WVFGRD96 47.0 245 70 -20 3.23 0.4352
WVFGRD96 48.0 245 70 -15 3.23 0.4349
WVFGRD96 49.0 245 70 -15 3.24 0.4303
WVFGRD96 50.0 245 70 -15 3.25 0.4267
WVFGRD96 51.0 245 70 -15 3.25 0.4324
WVFGRD96 52.0 245 70 -15 3.26 0.4350
WVFGRD96 53.0 245 70 -15 3.27 0.4323
WVFGRD96 54.0 245 70 -15 3.27 0.4250
WVFGRD96 55.0 245 70 -15 3.27 0.4264
WVFGRD96 56.0 245 70 -10 3.28 0.4318
WVFGRD96 57.0 245 70 -10 3.28 0.4289
WVFGRD96 58.0 245 70 -15 3.29 0.4226
WVFGRD96 59.0 245 70 -10 3.29 0.4237
The best solution is
WVFGRD96 21.0 240 75 -35 3.06 0.5007
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted. Each observed-predicted component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow. The lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
cut o DIST/3.3 -20 o DIST/3.3 +20 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.25 n 3
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| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
MODEL.01
Model after 8 iterations
ISOTROPIC
KGS
FLAT EARTH
1-D
CONSTANT VELOCITY
LINE08
LINE09
LINE10
LINE11
H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00